问某国人时如：they are Americans他们是美国人.为什么要加s

问某国人时如：they are Americans他们是美国人.为什么要加s They are near the river怎么问 某国人的单复数 如德国人 美国人 法国人等等 当回答是they are really friendly to us时,该怎么问? Do they go to the zoo?改为进行时.我知道是Are they going to the zoo?但是我想问,为什么Do要换成Are啊? 你是哪国人?译英.【 】【 】are you? the后加名词复数行吗问：What are they doing there?例：They are planting the trees.如有很多棵树,我不加s行不行,是回答问题. What are these?They are feet.为什么用They are 回答?我想问为什么要用they are 回答?而不用these are? they are having lunch at home.(踢问） .. 急问,do you think they are cheap对吗? They are teachers.(teacher下面划了横线)怎么问? 怎么问?才回答Yes,they are jumping They are they are Are they They are -------are they?they are --------(tomato) 1949年中国人口?如标题